Booklice, (Psocids)

Introduction:

Psocids are often called booklice or barklice because of their superficial resemblance to some lice species, and because they are often found on moldy books and papers in damp situations indoors, and under loose, damp bark outdoors. They are primarily nuisance pests in homes but are of considerable importance in insect collections, stored products, and food processing facilities. Their dead bodies in house dust are thought to contribute to asthma attacks. Psocids are found worldwide and throughout the United States, with about 287 species known from the United States.

Identification

Adults about 1/32-1/4" (1-6 mm) long; soft bodied, look like tiny termite workers. Head somewhat bulging, eyes varying from large and globose to a single ommaticlium/facet, ocelli present or absent. Antennae long, threadlike, 11-50-segmented. Prothorax reduced, necklike. Wings if present, 4 in number, membraneous (like cellophane), front wing larger than hind wing and often with pigmented spot/cell (pterostigma) along front edge before apex of vein R1, number of veins reduced and few crossveins; wings held rooflike over body at rest; wings showing various states of reduction to being absent. Tarsi 2- or 3-segmented. Cerci absent. Mouthparts chewing. Nymphs similar to adults in appearance but lack wings, although wing pads may be present.

Banded psocid, Liposcelis bostrychophila Badonnel; Liposcelididae. Adults (known only from females) pale to medium brown with yellowish tinge, head and thorax darker than abdomen; wingless; antenna 15-segmented (rarely fewer), with at least some segments annulated (ringed); compound eye with 7 ommatidia (facets); hind femur with a lateral protuberance, tarsi usually 3-segmented; found outdoors, litter of chick coups, common in old books in damp places and in stored grain; distributed worldwide, occurs throughout but scattered in the United States east of Rocky Mountains, and in western Canada.

Cereal psocid, Liposcelus decolor (Pearman) (=Liposcelus divinatorius (Muller), =Liposecelus terricolis (Badonnel)); Liposcelididae. Adults grayish white to medium brown with scattered darker spots on top of head and sides of thorax; female wingless; antenna 15segmented (rarely fewer), with at least some segments annulated (ringed); female compound eye with 7 ommatidia (facets); hind femur with a lateral protuberance, tarsi usually 3-segmented; found outdoors, in houses and warehouses, in stored grain and agricultural products; probably distributed worldwide, occurs throughout the United States except for the southeastern states.

Life Cycle

The typical psocid life cycle involves an adult period of sexual inactivity, courtship and copulation (several times in males, often only once in females), oviposition, egg hatch, and 46 nymphal instars. Eggs are laid either bare or encrusted, and with or without webbing over them. Nymphs resemble adults in form except for wings but lack functional ocelli, never have more than 2-segmented tarsi, and early instars have fewer antennal segments than adults. Nymphs of adults with extreme wing reduction tend to have 4 nymphal instars whereas, those of fully-winged adults tend to have 6 instars.

Probably the 3 psocids most commonly encountered in homes are the banded psocid, cereal psocid, and larger pale trogiid. Since more is known biologically about the cereal psocid, it is summarized here. At 80 degrees F (27 degrees C) and 65% RH, preoviposition lasts 2- weeks, eggs are laid 1 every 12 hours until about 75% of total are laid and then only occasionally, 3 larval molts occur, and adults live over 3 months; developmental period (egg to adult) requires about 1 month. In southern Louisiana, from October to January, at 50-87-F (10-30 degrees C), preoviposition lasts 31-54 days (average 45 days), 7-44 eggs are laid (average of 20 eggs), eggs require 11-27 days (average 21 days) to hatch, the life cycle (egg to egg) ranges from 111-130 days, and the postoviposition period lasts 1-24 days (average 9 days). However from June to August at 60-95 degrees F (16-35 degrees C), eggs average 6.9 days to hatch, an average of 57 eggs are laid, and the average life cycle (egg to egg) is 24.4 days. Average time to egg hatch is 21 days, 24-65 days are required to reach sexual maturity, and 24-110 days are required for the life cycle (egg to egg). They can overwinter in the egg or nymphal stage. This species is primarily parthenogenetic although males are known.